Ultra Wideband (UWB) systems transmit signals across a much wider frequency range than conventional systems. The bandwidth of the UWB signal may be equal to at least 20% of the center frequency or more than 500 MHz. UWB transmission operates by transmitting and receiving extremely short duration bursts of radio frequency (RF) energy. Each pulse is extremely short in duration, e.g., 0.1 to 4 nanoseconds (ns).
Devices known in the art for generating UWB transmission use diode-based pulse generators, typically including a step-recovery diode or a microwave-tunnel diode, which are triggered by a clock. In such configurations, although the diodes may have good switching or pulse-generation characteristics and can be tuned to cover a wide bandwidth, they are difficult to integrate, particularly in complementary metal oxide semiconductor (CMOS) devices.
Other UWB transmission devices known in the art, which may be used in high-power UWB radar transmitters, are based on pulsed-power technology, e.g., capacitive discharge circuits, transformer switches and transmission line switches, and/or light-activated semiconductor switches. These devices are generally expensive and difficult to integrate with CMOS. In addition, the high power limits for UWB radar transmission make this type of device unsuitable for use in commercial communication systems, for example, because of limits set by the Federal Communications Commission (FCC).
Another type of transmitter known in the art is based on a gated oscillator. In this approach, in which a local oscillator is gated, the center frequency of the spectrum can be controlled by the oscillator frequency; however, the gated oscillator approach is not flexible. For example, the center frequency cannot be digitally derived, the generation of multiple tones requires multiple phase-locked loops (PLL), and the PLL implementation may consume a significant amount of power, as it cannot be turned off between pulses to maintain loop stability.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn accurately or to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity or several physical components included in one functional block or element. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. Moreover, some of the blocks depicted in the figures may be combined into a single function.